1. Field of the Invention
The present invention relates to an image projection system capable of almost completely superposing the projection images of a plurality of original images by a plurality of image projection apparatuses without any image shift.
2. Related Background Art
For a conventional image projection system for superposing and projecting a plurality of projection images, the present assignee has proposed a projecting lens for increasing the brightness of a projection image in Japanese Laid-Open Patent Application Nos. 7-104186, 8-50241, and 9-21953. According to these proposals, the brightness of a projection image can be increased when a plurality of projection images are superposed and projected by a plurality of image projection apparatuses.
In these prior arts, however, no proposals for the entire system have been made, and how to obtain an image projection system optimum for use conditions by setting relationships such as the distortion characteristic of the projecting lens, the optical axis interval of projectors, projection magnification, and the size and pixel pitch of the original image has not been made clear.
It is an object of the present invention to solve the above-described conventional problem and provide an image projection system which can completely superpose and project a plurality of projection images without any image shift.
According to one aspect of the invention, an image projection system for projecting a plurality of original images to substantially the same region through separate projection optical systems, satisfies the following condition (1),
|K1| less than 0.25xe2x80x83xe2x80x83(1)
where
K1=xe2x88x92((L/xcex2)/H)*DISmax*0.0258/P
L: a maximum optical axis interval of the plurality of projection optical systems
xcex2: a projection magnification of the projection optical system
DISmax: a maximum value of absolute values of slope of distortion in the image height range of 0.25 to 1 when the maximum image height of the projection optical systems is normalized to 1
H: a short-side length of the original image
P: a pixel pitch of the original image.
In further aspect of the invention, at least one of the projection optical systems and the original images is movable in a direction perpendicular to an optical axis of the projection optical systems.
In further aspect of the invention, the following condition is satisfied in an entire variable focal length range of the projection optical systems, DISmax less than 1.5.
In further aspect of the invention, the plurality of projection optical systems for projecting the plurality of original images have the same or substantially the same distortion characteristic.
In further aspect of the invention, when in the plurality of projection optical systems, letting S1 be a maximum interval (maximum shift amount) of intervals each between an optical axis of each projecting lens and a center of the original image projected by that projection optical system, and H be the short-side length of the original image, a ratio K2 (=S1/H) of S1 to H satisfies the following condition (2),
0.35 less than |K2| less than 0.65xe2x80x83xe2x80x83(2).
In further aspect of the invention, the following condition (3) is satisfied,
|K1| less than 0.18xe2x80x83xe2x80x83(1xe2x80x2)
In further aspect of the invention, the projection optical systems each comprises a first lens unit having negative refracting power, a second lens unit having positive refracting power, a third lens unit having negative refracting power, a fourth lens unit having positive refracting power, and a fifth lens unit having positive refracting power sequentially from a screen side, and is designed to, in changing a focal length, move the second, third, and fourth lens unit in a direction of optical axis and adjust a focal position in accordance with a change in a distance from the projection optical system to a screen by the first lens unit, and the first lens unit has at least one aspherical lens.
In further aspect of the invention, the first lens unit has the aspherical surface on the screen side of a negative lens as a second component from the screen side.
In further aspect of the invention, a distortion in the projection optical system value of distortion in the projection optical system, is substantially constant in a range of image height used for projection.
One aspect of the invention provides an image projection apparatus having a projection optical system in which a distortion value of distortion is substantially constant in a range of image height used for projection.
In further aspect of the invention, the following condition is satisfied in an entire variable focal length range of the projection optical system in the image projection system,
xe2x80x83DISmax less than 1.5.